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Let hull dry after sandblasting - how long?

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Let hull dry after sandblasting - how long?

Old 05-15-2020, 07:21 AM
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Default Let hull dry after sandblasting - how long?

Having 12 years of bottom paint sandblasted off our boat this weekend. We were told by the company to let the hull dry out for about a week before applying epoxy primer and bottom paint. I.E.: " You'd be surprised how much moisture stays trapped under bottom paint even after being out of the water all winter" - sandblast guy. Is this true?
Old 05-15-2020, 08:00 AM
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I just got quotes to do this last month, but I havent pulled the trigger due to other stuff. I have about 20 coats. The guy told me to wait a week before I paint. He is in west palm, could be the same guy lol.
Old 05-15-2020, 08:02 AM
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i like to do them before the winter and let them sit weeks, its also important to give it a good soap and fresh water wash - not just a pass with a pressure washer to insure you have removed all the salt so any moisture that may be there can dry out
Old 05-15-2020, 08:25 AM
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This is in NJ so not the same guy. Letting it sit over the winter is no longer an option (No one seemed to want to sandblast over the winter here.) Most of the bottom paint has been off for a few weeks. It's only 30% primer coat that is getting blasted off. One of the workers said wait a week. The owner said you can paint tomorrow if you want. I'll probably do the taping and a good clean with dish soap and power washer tonight. Any DIY way to test moisture? Being in the water by memorial day would be nice.
Old 05-15-2020, 08:35 AM
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Tape a piece of plastic ( visquene, piece of sandwich bag, etc ) down on surface with duct tape around the edges and see if moisture forms underneath.
I have never done it on a boat but, have on other surfaces
Not in direct sunlight. Its been awhile , I forget stuff.

Last edited by jdwaters; 05-15-2020 at 08:43 AM.
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Old 05-15-2020, 08:51 AM
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sounds legit.
Old 05-15-2020, 08:54 AM
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Fiberglass absorbs a little water so I think he is giving you good experienced advice.The epoxy can trap water on the opposite side (bilge) and will not dry until the epoxy comes off the outer skin. The time depends on the thickness of the hull imo. but if a pro says a week, I'd go with that.

A power washer will probably drive water back deeper into the laminate than a brush and a hose.
Old 05-16-2020, 05:34 AM
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Well here's the before and after. After fighting it with everything from powerwashing to paint stripper, I can say this was well worth the 700 bucks. Came out rougher than I thought. I couldn't imagine trying to get the gelcoat back to a shine but it's getting bottom paint anyway. The guy said hydrasports does a good job of laying a thick gelcoat so there isn't much blistering. 70's bertrams are another story... I have some minor blistering but nothing a little marine tex can't take care of.



Old 05-16-2020, 05:53 AM
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dont use marine tex for those, get some epoxy filler from whatever company you planned on priming with, if interlux get the watertight filler. also suggest at least one coat of primer FIRST, then start filling, add more primer on top of that
Old 05-16-2020, 05:56 AM
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Im getting ready to havemy boat done here in a few weeks. I wasnt given any advice on a dry time afterwards but im glad i found this post. Im gonna give mine a couple weeks of dry/ cure time before doing any fiberglass repairs or painting/gel coat work.
Old 05-16-2020, 05:57 AM
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Why not use marine tex? Doing pettit epoxy barrier coat and pettit vivvid.
Old 05-16-2020, 06:39 AM
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Originally Posted by soapysundays View Post
Why not use marine tex? Doing pettit epoxy barrier coat and pettit vivvid.
It's not the right tool for the job. Taking Raybo's advice when it is given will serve you well.
Old 05-16-2020, 07:11 AM
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Originally Posted by soapysundays View Post
Why not use marine tex? Doing pettit epoxy barrier coat and pettit vivvid.

Pettit | EZ-Fair


EZ-Fair Epoxy Fairing Compound 7050 is a lightweight, two-part epoxy putty designed for filling and smoothing surface imperfections above and below the waterline. The special resins used in EZ-Fair impart a high degree of water and chemical resistance to the product, making it an integral part of the Pettit Gelcoat Blister Repair System. In addition, EZ-Fair is the product of choice for fairing metal keels or any underwater surface. Use it for leveling uneven surfaces, filling gouges, scratches, or other damage on fiberglass, wood or metal surfaces. It’s excellent chemical and water resistance make it the ideal choice for repairing blistered gelcoat in an osmotic blister repair system. EZ-Fair is non-sagging and non-shrinking and sands to a smooth finish. The quick-cure formula allows for multiple coats to be applied and sanded in a single day.
Old 05-16-2020, 08:27 AM
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You mentioned some minor blistering. Open those up right away as those areas will need the most time to dry before filling.
Old 05-16-2020, 09:47 AM
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Thanks for the advice. Going to see if I can find some of the pettit ez fair locally. Hopefully west marine has it or else it's looking like no boat for memorial day. The blisters were pretty well opened by the soda blasting and my prior methods so it's been exposed for a while now.
Old 05-16-2020, 10:44 AM
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you have gone this far you cant rush this otherwise you are wasting your time
you can use another brand of epoxy filler if they have that locally, that wont matter at all


Old 05-16-2020, 11:43 AM
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Even if it's being bottom painted - No marine tex? Sorry for questioning. I keep seeing THT post about no problems using it if you're bottom painting.
Old 05-16-2020, 01:10 PM
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After the blast this bottom should be washed every other day. Fresh water washing helps dissolve the "blister juice" which is partly glycol and nothing will stick to glycol. It also helps to get rid of the salt, and as you may know, when your shirt or towel goes over the side you will not get it truly dry until you get rid of the salt. Also, believe it or not, fresh water rinses promote drying.
Old 05-16-2020, 05:29 PM
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Originally Posted by soapysundays View Post
Even if it's being bottom painted - No marine tex? Sorry for questioning. I keep seeing THT post about no problems using it if you're bottom painting.
it sands like shit, it isn’t the right product for this application, and it will cost you more money
yes it’s epoxy and you seem like you really want to use it for the sole purpose of connivence to rush the process so go ahead and use it.
Old 05-16-2020, 05:41 PM
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Originally Posted by jdwaters View Post
Tape a piece of plastic ( visquene, piece of sandwich bag, etc ) down on surface with duct tape around the edges and see if moisture forms underneath.
I have never done it on a boat but, have on other surfaces
Not in direct sunlight. Its been awhile , I forget stuff.
jdwaters is correct. It’s a legit test we do to test for moisture in concrete floors before applying coatings. If you have a heat lamp, shine it on the plastic for a couple hours. Take it away and let the plastic on for a total of 24 hrs. Any, repeat any, moisture on the underside of the plastic indicates moisture in substrate. Remove the plastic and wait 3-4 days and repeat until no moisture is seen.

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